Colloidal transport near surfaces, which gives rise to a particle-free region known as the exclusion zone (EZ), plays a critical role in applications such as water purification, mechanical sorting, and energy storage. In ionic solutions near ion-exchange membranes, diffusiophoresis is known to be the primary mechanism driving the colloidal particles away from the surface, forming an EZ that can extend hundreds of micrometers. However, the development of the EZ is accompanied by the emergence of a particle-rich layer, which can trigger a flow instability reminiscent of the Rayleigh-Taylor instability. In our current vertically configured system—with the membrane positioned atop capillaries filled with colloidal suspension—such a flow instability results in a mixing region below the exclusion zone. We combine experiments with numerical modeling to explore the dynamics of EZ formation and to identify the mechanisms governing the onset and suppression of this instability. In particular, we assess the impacts of suspension properties – such as, particle surface chemistry and colloidal and ionic concentrations – as well as geometrical factors. Our preliminary results indicate that while EZ dynamics remain largely unaffected by colloidal concentration and capillary geometry, these factors significantly influence the onset of instability.
